As is well known in the art, the windshields for automotive vehicles are comprised of two sheets of glass with a thermoplastic substance, typically polyvinylbutyral intermediate film interposed therebetween bonded integral into one sheet of glass so that the scattering of broken glass pieces resulting from the damage of the windshield can be prevented.
Frequently, a portion of an intermediate film is colored so that the windshields may have the additional function of sun visors.
Of the various methods for dyeing decorative intermediate films for laminated glass sheets, a transfer method (disclosed, for instance in Japanese Patent Publication Nos. 55-14821 and 57-29426) has been used. According to this method, a transfer sheet, which is extended over a surface of a substrate and is printed with an ink capable of dyeing an intermediate film, is superposed over an intermediate film, and then is subjected to a heating and pressure application process so that the printing ink is transferred over the intermediate film. After the separation of the substrate and ageing or only after ageing, the printed pattern is transferred over the surface of the intermediate film.
However, according to the above-described method, in the process of applying heat and pressure to an intermediate film in the transfer method, it frequently occurs that fine projections and recesses formed over the surface of the intermediate film disappear so that this method has the defect that air bubbles tend to be left when the intermediate film thus obtained is laminated to a sheet of glass. That is, unless such fine projections and recesses over the surface of the intermediate film are left in order to carry out the deairing operation when the glass sheets are laminated, defective articles containing air bubbles are frequently produced, and consequently, the yield is decreased.
Furthermore, in the conventional processes for manufacture of intermediate films, the penetration of ink is limited to the portion immediately adjacent to the surface of a glass sheet so that the overall surface of the intermediate film is not satisfactorily dyed, and consequently, there arises the problem that the outer appearance of the finished product is degraded. That is, in the case of forming a coloring pattern, the conventional processes are limited in their capability of forming a high-quality printed pattern (for instance, a vignette pattern).